Sensational Findings on Breede River Bull Shark Migration
In 2009, a 4m Bull shark was captured in the Breede River estuary in the Southern Cape region of South Africa, at the time representing a new global size record for the species. The Bull shark (known locally as the Zambezi shark) is well known worldwide for swimming far up rivers, thriving in low-saline water, but until now has only been documented several hundred kilometres further to the north-east. Although there have been sightings of Bull sharks in the Breede River over the years, some locals dispute their existence and documented evidence has been scarce.
The report of Bull shark activity in the South-Western Cape was therefore exciting news to local marine scientist, Meaghen McCord of the South African Shark Conservancy (SASC), who initiated a research project to establish the nature of the Breede River population.
Said McCord “ this project began as an exploratory expedition to determine what species of sharks were using the Breede River estuary. We were extraordinarily lucky to find the system was home to some of the largest Bull sharks ever recorded in South Africa, as well as being the most southerly distribution for the species in the country.”
In March 2011, after two years of examining the behaviour and movement of Bull sharks in the estuary, a large male was captured and tagged with a Pop-up Archival Transponding (PAT) tag to record the seasonal migration of the shark as it left the river before winter. The tag is attached to the shark in the dorsal fin area and set to release from the host after a period of time, whereafter it floats to the surface and transmits data via satellite.
Up to now it has only been speculated as to where the Breede River population of Bull sharks migrate, if at all, as very little has been studied on the African populations of these sharks, other than recordings made by the Natal Sharks Board via their beach netting program along the coast of kwaZulu-Natal.
“We are slowly beginning to gain insight into how this apex predator utilises river systems” said McCord. “This is the first time the ecology and behaviour of Bull sharks has been studied in South Africa and we hope it assists with the development and implementation of management measures for this near- threatened species.”
The tagging of the shark in March of this year, made possible by a research grant from the Save Our Seas Foundation, was very important to establish if the Breede River population was endemic to the area or indeed part of the larger population and, therefore, global gene pool.
In May, two months after tagging the shark, the first satellite transmission was made off the coast of Mozambique, near the island of Bazaruto. This was more exciting than anyone had expected, as it revealed a journey of over 2000km, or 36 km per day! A significant discovery by any means, it gives a glimpse into the extraordinary range of these sharks and how local conservation practices can have international implications.
“Despite being listed by the IUCN as near-threatened globally, there are no existing management or conservation measures for Bull sharks in SA or Mozambique “ said McCord. “We have now shown this species migrates across international borders, whereby it becomes vulnerable to a multitude of fisheries and environmental pressures”.
According to McCord, it is vital to obtain temporary protection of the Bull shark in the Breede River system, until it can be studied further. “It is widely recognised that estuaries play a critical role in the life-history of this species, and we feel that affording a degree of protection to Bull sharks in their southernmost habitat will play a vital role toward maintaining ecosystem integrity in African waters, “ she said.
“A special thanks to all who have assisted with funding and supporting this project,” said McCord, “including:
DAFF, DEA, Lower Breede River Conservancy, White Shark Projects, Western Province Shore Angling Association, and our primary sponsors, the Save Our Seas Foundation.”